As a rule, a processing apparatus for photographic sheet material comprises several vessels each of which contains a treatment liquid, such as a developer, a fixer and a rinse liquid. As used herein, the term sheet material includes not only photographic material in the form of cut sheets, but also in the form of a web unwound from a roll. The sheet material to be processed is transported through these vessels in turn, by transport means such as one or more pairs of drive rollers, and thereafter optionally to a drying unit. The time spent by the sheet material in each vessel is determined by the transport speed and the dimensions of the vessel in the sheet feed path direction.
In a conventional processing apparatus the sheet material is transported along a generally horizontal feed path, the sheet material passing from one vessel to another usually via a circuitous feed path passing under the surface of each treatment liquid and over dividing walls between the vessels. However, processing machines having a substantially vertical orientation have also been proposed, in which a plurality of vessels are mounted one above the other, each vessel having an opening at the top acting as a sheet material inlet and an opening at the bottom acting as a sheet material outlet or vice versa. U.S. Pat. No. 4,166,689 (Schausberger et al. assigned to Agfa-Gevaert AG) describes such an apparatus.
It is known in the art to perform the rinsing of a silver halide photographic material which has been developed and fixed, by means of a "cascades" rinsing station which comprises two or more rinsing tanks through which the material is passed in succession, the rinsing liquid flowing in counter-current. The advantage is that the last rinsing tank will contain almost fresh rinsing water so that silver effluent will be small. Cascade processing of sheet materials with other processing liquids, such as developers or fixers, also has advantages.
Such a cascade rinsing arrangement is known in which a pump is provided for feeding liquid to the last cell and further pumps are provided for transferring liquid from each cell to its preceding cell. The provision of a pump between each pair of adjacent cells is costly, especially bearing in mind that such pumps represent a significant proportion of the cost of the total apparatus.
While the use of pumps in a horizontal processing apparatus can be avoided by an overflow cascade, liquid levels would be different in different cells and difficult to control in view of surface effects.